Covalent coupling of a novel TLR7 agonist to antigen elicits an effective immune response in a murine melanoma tumor model

3019 Background: Toll-like receptor (TLR) signaling triggers innate immune stimulation capable of generating an adaptive immune response under appropriate conditions. TLR agonists have shown efficacy in preclinical and clinical cancer therapies. However, one limitation to this approach has been the use of TLR agonists delivered at distances away from the target (ie-subcutaneous injections for general immune stimulation) or the inability to effectively couple antigen with adjuvant. Methods: We have synthesized a novel TLR7 agonist capable of covalent coupling to primary amines under physiologic conditions. In vitro activity of adjuvant alone or antigen-adjuvant complexes were tested for innate immune activation by utilizing bone marrow-derived murine or peripheral blood mononuclear cell-derived dendritic cells (DC) with respect to DC maturation and cytokine secretion (IL12, IL6, TGFbeta and IFNgamma). Immunocompetent syngeneic C57/b6 mice were prophylactically vaccinated with intradermal with either antigen, antigen mixed with adjuvant or antigen- adjuvant coupled complexes and challenged with B16 melanoma tumor cells expressing the cOVA transgene. Results: The effective concentration (EC50) for each compound generally followed a bell shaped distribution with higher doses being inhibitory. Maximal stimulation occurred between 10 and 1000nM. Coupled adjuvant molecules retained activity with generally lower EC50 values. Coupling 1V199 to chicken ovalbumin nearly doubled median survival from 22 to 35 days following subcutaneous tumor challenge compared with chicken ovalbumin alone. Conclusions: Covalent linkage of a TLR7 agonist to antigen stimulates DC cytokine production and protects mice from tumor challenge. Use of a soluble TLR7 agonist which retains its immune stimulating properties following coupling to antigen under physiologic conditions may be useful in the development of an in situ vaccine in solid tumor therapy. No significant financial relationships to disclose.